An apparatus for high volume, accurate cutting of both hard and soft materials using a fluid jet cutting device is well known in the art. Furthermore, the use of controlled cutting systems having omni-directional capability using water as a cutting agent are also commonly known as set forth in U.S. Pat. No. 4,786,848, issued Nov. 22, 1988 in the name of Nickerson, and assigned to the assignee of the subject invention. In this technology, a stream of high pressure water is utilized to remove excess material from the workpiece or part being processed. Such water jet cutting systems have successfully been used to cut materials such as composites, corrugated paper board, asbestos, asphalt-based materials, foamed plastics, rubber, nylon, mineral fibers, fiberglass and fiberglass-reinforced plastics, high pressure laminates, plywood, chips in board, poly-ethylene sheet, apparel and automobile fabrics, and food and confectionery products.
The basic components of the water jet process includes directing clean water flow to a booster pump, through filters, into an intensifier, through tubes and swivels, thence to a cutting nozzle. The pressurization of the water is obtained by using fluid pressure intensifier principles. This principle is best illustrated by the force equilibrium of a double-acting piston having a piston end and two smaller diameter plungers. Hydraulic oil pressure acting on the piston results in a force on the plunger that pressurizes water in a small diameter chamber. Since the intensification ratio is constant by virtue of the fixed piston to plunger diameter ratio, water pressure can be regulated by controlling the hydraulic oil pressure. The booster pump has a 10, 5 and 1 micron filter and pumps the water to 190 PSI to preload the pump or intensifier high pressure cylinders. A cutter nozzle arrangement usually consists of a pneumatically controlled shut-off valve, nozzle tube, a jewel orifice and a stainless steel holder and nozzle nut.
In this construction, a workable constant cutting pressure must cut the workpiece within the predetermined required cycle time to meet production volume, plus achieve the quality standards of the cut workpiece. The value of the workable cutting pressure is determined by a balance of constant and variable factors that govern the design of the application program including material type; material thickness versus constant cutting pressure, cycle time, and jewel orifice size; cut quality standard versus constant cutting pressure and cycle time; cycle time versus constant cutting pressure and jewel orifice size; and jewel orifice size versus constant cutting pressure. Since the workable constant cutting pressure will be set to produce desired cut standards through most of the workpiece, there can be variations in thickness or material types in the workpiece that can result in lesser cut quality. Examples of other variables that can affect cut quality include cycle time that is restricted due to insufficient cutting pressure in some areas; further, quality can be adversely affected in some areas due to selecting a constant cutting pressure that is an excessive pressure for a particular cut. These problems have been especially pronounced in the past because water jet cutting apparatus has been unable to produce variable pressure jets matched to different cutting requirements on a single workpiece. In such prior apparatus, the cycle time can be restricted by insufficient cutting pressure, i.e., slower machine feed rates in the thicker areas to obtain a clean cut, and increased feed rates in thin, long straight areas. Furthermore, cut quality can be affected by excessive cutting pressure, i.e., slower machine rates for detail areas or induced water saturation can occur in some applications. Such saturation can cause workpiece delamination and/or staining, and scoring of substrate backing in composite workpieces.